1. Field of the Invention
The present invention relates to an apparatus and method for servo control of an optical disk driver, and more particularly, but not by way of limitation, to a servo control apparatus and method capable of an optical disk driver compensating for eccentric rotation of the disk.
2. Description of the Related Art
Shown in FIG. 1 is a general optical disk player, including an optical pickup 2 for reproducing signals from an optical disk 1, an R/F unit 3 for equalizing and shaping the RF signals reproduced from optical disk 1 by pickup 2, and a synchronization unit 7 for creating a clock signal whose phase is synchronized with the binary data outputted from R/F unit 3. The disk player also includes a digital signal processing unit 4 for processing the binary data stream received from R/F unit 3 in order to retrieve digital data using the synchronization clock, an MPEG decoder 5 for decoding the retrieved digital data to obtain original picture or audio data, and a sled motor 11 for moving optical pickup 2. The disk player further includes a spindle motor 12 for rotating optical disk 1, a driver for driving sled motor 11 and spindle motor 12, and a servo unit 6 for controlling optical pickup 2 and driver 8. A microprocessor 9 supervises overall operations of servo unit 6 and digital signal processing unit 4, and a memory 10 stores data necessary for microprocessor 9.
In the optical disk player, when optical disk 1 is inserted into a disk tray, optical disk 1 is clamped by a clamping device. Then, controlled by servo unit 6, the driver 8 provides electric current to rotate the spindle motor 11, and maintains the rotation velocity of optical disk 1 constant, at about 2,500 rpm.
To reproduce signals recorded on optical disk 1, optical pickup 2, with a laser diode LD and photo diodes PD installed in it, forms a laser beam spot on the recording layer of optical disk 1 by irradiating a laser beam emitted from the laser diode LD. The laser beam reflected from optical disk 2 is collected by the photo diodes PD and converted into electric signals. R/F unit 3 equalizes and shapes the electric signals to produce binary data, and digital signal processing unit 4 performs the processing of the binary data. The synchronization clock necessary for digital signal processing unit 4, synchronized with the binary data from R/F unit 3, is provided by synchronization unit 7.
The basic role of sled motor 11 is to move optical pickup 2 in the radial direction. Controlled by servo unit 6, sled motor 11 moves optical pickup 2 rapidly in the radial direction in the track search mode for locating a desired track. If the track search mode is set by a user""s request, microprocessor 9 detects the position of the track which optical pickup 2 is currently accessing, calculates the distance between the present track and destination track, and issues a command to move optical pickup 2 to the destination track by jumping the calculated distance.
In the aforementioned track search operation, the distance that optical pickup 2 should jump is calculated on the condition that the center of the objective lens in optical pickup 2 coincides with the optical axis. In reality, however, this condition is not usually satisfied since the objective lens is suspended from the tracking actuator, and can move within a certain range amounting to 200-300 tracks. Hence, unless the movement of the objective lens is taken into consideration, the desired track cannot be reached, even though optical pickup 2 jumps exactly the calculated distance.
As shown in FIG. 2(a), because of disk clamping errors, the center of the disk does not usually coincide with the axis of disk rotation, which creates eccentric rotation of the disk. Also, owing to imperfect disk manufacturing processes as shown FIG. 2(b), the tracks formed on the disk are not ideal spirals. This causes distortions in reproduced signals.
Due to the eccentric rotation of the disk caused by disk clamping errors and imperfect disk manufacturing processes, the destination track repeatedly moves inward and outward with respect to optical pickup 2 as the disk rotates. This makes the task of jumping to the destination track difficult and causes track jump errors.
If a pause mode is set while track-following control is being performed, each time the disk rotates one revolution, the optical beam spot is controlled to move 1 track inward so that the beam spot remains on the desired track. In the case where the beam spot deviates from the track center as at points (a) or (c) shown in FIGS. 3 and 4, it may take a longer time for the beam spot to settle in the destination track, or the track jump may fail.
It is an object of the present invention to provide a method for servo control of an optical disk driver, capable of measuring the amount of disk eccentricity caused by imperfect disk manufacturing processes or disk clamping errors, and capable of compensating for the disk eccentricity with the result that stable track search operations are guaranteed.
Accordingly, the present invention is directed to a method and apparatus that substantially obviate one or more of the problems due to limitations and disadvantages of the related art.
In accordance with the purpose of the invention, as embodied and broadly described, one aspect of the invention includes detecting an amount of disk eccentricity from a main beam reflected from an optical disk; setting compensation values corresponding to the detected amount of disk eccentricity; and adjusting a number of tracks to be crossed during a track jump operation using the compensation values.
In another aspect, the invention includes detecting an amount of misalignment between a center of an objective lens and an optical axis of a photodetector; calculating a value used to move an optical pickup to a destination track; and adjusting the calculated value based on the detected amount of misalignment.
In still another aspect, the invention includes detecting a tracking error signal from an optical disk; and determining when to move the beam spot based on the tracking error signal.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.